1. Field of the Invention
This invention relates generally to a method and apparatus for testing of substrates and, more particularly, to a ceramic substrate tester and a glass ceramic substrate tester having substrate location clamping, sensing, and contacting.
2. Discussion of the Related Art
Substrate testers are known in the art for performing network integrity tests on substrates. A substrate refers to a packaging unit that provides an interface between a semiconductor chip (e.g. a very large scale integrated (VLSI) circuit chip) and a higher level packaging unit (e.g., a printed circuit board). A network is generally defined by a set of one or more electrically connected common points on a substrate. Networks are used to distribute electrical signals and voltages externally and/or internally about the substrate in accordance with the requirements of a particular integrated circuit chip. Substrate testers are used during substrate manufacturing to guarantee that there are no process or design created defects (corresponding to opens or shorts) on a particular substrate being tested. Typically, a substrate tester performs a test using a particular contacting scheme. A test matrix controller (or test engine) is then used to provide an electrical stimulus on each point of the networks contacted by the contacting scheme and then systematically scans the remaining points in the test matrix to guarantee all desired connections exist (opens test) and that there are no unwanted connections (shorts), as the case may be.
Glass ceramic substrates for packaging of VLSI ICs are fragile and costly to produce. In the testing of substrates, it is desirable for the tester to receive the substrate (or product) to be tested in such a way that the substrate, tester and test head(s) will not incur damage. Undesired damage can occur if the substrate is not correctly seated in the tester during the testing thereof. For example, undesirable damage to the substrate can be caused when the substrate or product under test is ajar, mispositioned, or otherwise hung up within the test station of the substrate tester. In addition, undesired damage can also occur if the substrate, during a loading or movement of the substrate within the tester, slides against the tester contacts, or probes, of the test head(s), thereby deforming the tester contacts or probes. In other words, damage to the tester test probes can also occur when the substrate being tested is ajar, mispositioned, or otherwise hung up within the test station. Tester head or probe damage is a significant expense in terms of repair and/or replacement. Note also that testing of a substrate can include front side (top) and/or back side (bottom) testing.
In known testers, the product is loaded within stationary position locators of the tester. The test head pins (i.e., contact probes) are exposed to undesirable X-Y deformation and damage during product loading in preparation for testing. Once a substrate is loaded in a desired position, the tester then compresses the test head pins in a Z-axis direction against the product under test. Any anomalies in product thickness can cause the compression to vary greatly from one product to another. Typically, the surface of the product is stationary and the test head pins are lowered to the product surface without regard to any variation in product thickness or non-planarity.
In addition, with respect to known testers, contactors (i.e., test heads) move in and out of the test station to allow an operator to load a part (i.e., product and/or substrate) to be tested. The mechanical movement in and out causes the cabling associated with the test heads to continually bend and flex. Bending and flexing of the test head cabling causes broken conductors, which leads to costly repairs. In addition to the actual cost of the cabling, the costly repairs also include costs associated with equipment down time which are incurred until repairs can be made.
Still further, in other approaches, the substrate part to be tested is placed on top of an array of spring plunger probes, wherein the probes are compressed against test pads on the substrate or product. This approach, however, increases the opportunity for movement of the product. Movement of the product is not desirable since any movement would cause the product to scrape against any contacting surfaces, for example, of a locating nest or position locator. As a result, the spring plunger probe arrangement contributes to incidents of broken product, damaged product and damaged equipment.
It would thus be desirable to provide a method and apparatus for elimination of damage to product and to test probes resulting, for example, from product being ajar or otherwise hung up in a test station. Furthermore, it would be desirable to provide a mechanism to prevent damage due to mispositioned product in a substrate tester. Still further, it would be desirable to provide a substrate tester capable of loading and unloading a substrate to be tested quickly and accurately without damage.